How do I size airflow for a duct heating coil?

Enter room heat loss and desired supply/off-coil temperature. Airflow = heat duty / (ρ × cp × ΔT).

What off-coil temperature should I use?

Typical supply air 30–50°C for comfort heating. Higher off-coil temperatures reduce airflow but increase stratification risk — check throw and room layout.

How does this relate to AHU coil sizing?

This is a single-zone check. Full AHU sizing must include fresh air, latent loads, and frost protection — use the AHU coil capacity calculator for complete duties.

BuildFlo Design Guide · Thermal · CIBSE Guide B

Duct coil heating calculator

Size ducted heating coil airflow or off-coil temperature from heat loss. Free duct coil heating calculator for AHU and FCU design.

What this calculator does

Duct coil heating helps UK building services engineers with room airflow or off-coil temperature from heat loss via ducted coil. The calculation follows CIBSE Guide B methods used in everyday MEP design — enter your project inputs below for a first-pass result.

Whether you searched for "duct coil heating", "duct coil heating calculator", or "how to duct coil heating", this page gives you a working tool plus the context to use it on a real job.

When to use it

Use this for early-stage sizing and sanity checks on UK building services work. It is not a substitute for issued calculations — verify against the project specification, drawings, and relevant standard before sign-off.

How to use it

1. Fill in the inputs for your scenario (defaults are starting points only). 2. Click Calculate — results include the method and assumptions where applicable. 3. Verify against the project specification and relevant standard before issuing.

Typical output unit: l/s.

Tips

Defaults are indicative — replace with project-specific values from the architect, structural, or MEP spec.
For issued calculations, save results in your BuildFlo project and attach to the calculation folder.
Need the regulation citation? Open BuildFlo chat in the app and ask about duct coil heating under UK standards.

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Frequently asked questions

How do I size airflow for a duct heating coil?: Enter room heat loss and desired supply/off-coil temperature. Airflow = heat duty / (ρ × cp × ΔT).
What off-coil temperature should I use?: Typical supply air 30–50°C for comfort heating. Higher off-coil temperatures reduce airflow but increase stratification risk — check throw and room layout.
How does this relate to AHU coil sizing?: This is a single-zone check. Full AHU sizing must include fresh air, latent loads, and frost protection — use the AHU coil capacity calculator for complete duties.